Because you cannot immediately think of a study does not mean one is not possible.
Consider: Measure changes in parents during child-rearing and correlate with measures of amount and style of "care" given to children. Are those that are more caring parents happier, on average, than those who are not? Control for anything you can think of controlling.
Consider: Measure changes in parents during child-rearing and correlate with measures of amount and style of "care" given to children. Are those that are more caring parents happier, on average, than those who are not? Control for anything you can think of controlling.